mineral
Limonite (Iron Ore)
FeO(OH)·nH2O
AI-generated identification · may be incorrectHardness: 4-5.5 (Mohs scale), Color: Dirty yellow to yellowish-brown, Luster: Dull to earthy (may appear sub-metallic if wet), Crystal Structure: Amorphous (often pseudomorphic after other minerals), Cleavage: None
- Hardness
- 4-5
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Physical properties
Hardness: 4-5.5 (Mohs scale), Color: Dirty yellow to yellowish-brown, Luster: Dull to earthy (may appear sub-metallic if wet), Crystal Structure: Amorphous (often pseudomorphic after other minerals), Cleavage: None
Formation & geological history
Formed primarily as a secondary mineral through the weathering and oxidation of other iron-bearing minerals like pyrite, magnetite, and siderite. Often found in bog deposits or gossans (iron-rich caps over ore bodies).
Uses & applications
Historically used as a common iron ore and as a source of yellow pigment (yellow ochre) for paints and dyes. Today, it is primarily an indicator for prospecting deeper ore deposits.
Geological facts
Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It was the material famously used for cave paintings by early humans.
Field identification & locations
Identify by its distinct yellowish-brown streak and lack of cleavage. It is commonly found in sedimentary basins and weathered rock outcrops. Often feels denser than an average stone of the same size.
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